Sam, for full grown Cherimoya trees, they need very little Nitrogen input. Stopping Nitrogen input around September will help to control the overall size of the tree.
For my fruiting size Cherimoya, I feed it with 3-12-12 once a month throughout the year except October through March or April when the tree is beginning or in dormancy. I also feed it my Cherimoyas with Kelp emulsion, coffee grounds, earthworm castings and compost.
Mark, Cherimoya trees are pretty much Evergreen trees in SoCal except the months of March and April but this depends on where you are(climate) and how you care for your trees. If you do nothing, the tree may stay green and hold leaves year round.
I back off on Nitrogen fertilizer and watering around October because of our Winter rains and I significantly back off on watering around March. This is specific to where I live and I look for clues from my tree to tell me when to prep it to go dormant.
I prep it for dormancy when all the fruit are off the tree and the tree shows signs of pulling nutrients back from the leaves. The leaves will start to look like it is getting some interveinal chlorosis. Leaves will also start drying up and dropping on its own.
After it’s dormancy period, you will know when to gradually increase watering and fertilizing because you will see new growth or swollen buds from where the leaves have fallen off.
When the Cherimoya tree comes out of dormancy, the flowers will usually appear on the new growth.
Simon